A microphone array device obtains a target sound from a target sound source. The microphone array device uses, for example, a synchronous subtraction method illustrated in FIG. 26 and a method illustrated in FIG. 27. FIGS. 26 and 27 illustrate microphone array devices of related technologies.
A microphone array device 01 in FIG. 26 includes a microphone MIC1 and a microphone MIC2. In FIG. 26, a sound reception direction is set at a left side of the microphone MIC1. Meanwhile, a suppression direction is set at a right side of the microphone MIC2. The sound reception direction includes a target sound source SS. The suppression direction is a direction opposite to the sound reception direction. Both the microphone MIC1 and the microphone MIC2 are non-directional microphones that do not control directivity.
A delay unit 1 delays a sound signal that includes noise obtained by the microphone MIC2 for a certain delay time. A subtraction unit 2 subtracts an output signal of the delay unit 1 from a sound signal that includes a target sound obtained by the microphone MIC1. The microphone array device 01 is configured as a device with directivity that is illustrated by the dotted line in FIG. 26 according to the above-described synchronous subtraction method. In other words, the microphone array device 01 suppresses noise from the suppression direction. The microphone array device 01 may obtain a target sound from a target sound source SS.
A microphone array device 02 in FIG. 27 includes a microphone MIC1 and a microphone MIC2. In FIG. 27, a sound reception range is set at a left side of the microphone MIC1. A shift range and a suppression range are set at a right side of the microphone MIC2. The sound reception range is a range that includes a target sound source SS. The suppression range is a range that is different from the sound reception range. The microphone array device 02 suppresses noise generated from a sound source that is included in the suppression range. The shift range is a range that is set between the sound reception range and the suppression range. Moreover, the shift range is where a degree of suppressing noise is gradually shifted between the sound reception range and the suppression range.
An FFT3a applies Fast Fourier Transform (FFT) to convert a sound signal obtained by the microphone MIC1 into a complex spectrum IN1(f) on a frequency axis. Likewise, an FFT3b applies Fast Fourier Transform (FFT) to convert a sound signal obtained by the microphone MIC2 into a complex spectrum IN2(f) on a frequency axis. A phase spectrum difference calculation unit 4 calculates a phase spectrum difference DIFF(f) between the sound signal obtained by the microphone MIC1 and the sound signal obtained by the microphone MIC2 based on the complex spectrum IN1(f) and the complex spectrum IN2(f). The microphone array device 02 may identify a range where a sound source is included for each frequency by the phase spectrum difference DIFF(f). A gain calculation unit 5 calculates a noise suppression gain G(f) based on the identified range of the sound source. The noise suppression gain G(f) is a variable to determine an input and output ratio. The microphone array device 02 determines how much noise is suppressed by adjusting the noise suppression gain G(f). A noise suppression unit 6 calculates an output OUT(f) in which noise is suppressed based on the complex spectrum IN1(f) and the noise suppression gain G(f). An IFFT7 applies reverse FFT to the output OUT(f) to obtain an output. The microphone array device 02 may obtain a target sound from the target sound source SS while suppressing noise.
The above-described related technology is discussed, for example, in Japanese Laid-open Patent Publication No. 2007-318528.